The next generation of microelectronic devices will require an increase in the density of circuit elements per unit volume. As the distance between the metal lines decreases, there will be increased problems due to capacitive coupling (cross talk) and propagation delay. This problem can be avoided or minimized if the circuit wires are separated by insulator layers of increasingly lower dielectric constant. Because of these requirements, attention has been focused on developing porous dielectric materials. One such class of materials are zeolitic materials, and especially virtually aluminum free zeolitic materials.
For example U.S. Pat. No. 6,329,062 B1 discloses a two component porous material including small silicalite crystals in a porous binder which provides a low dielectric constant material useful as an insulating layer in microelectronic devices. The silicalite nanocrystals are smaller than the characteristic dimensions of the features on the integrated circuit device, while the binder is an amorphous porous material that links the silicalite nanocrystals together. The '062 reference states that the aluminum concentration in the silicalite is to be less than 1 part in 10,000 (0.01 wt. %). U.S. Pat. No. 6,533,855 B1 discloses the chemical modification of the surface of silicalite and high silica zeolite nanoparticles permitting such particles to be dispersed in non-polar hydrophobic solvents which can then be used to form interlayer dielectric layers. U.S. Pat. No. 6,573,131 B2 discloses a process for producing a silica zeolite film on a semi-conductor substrate in which a zeolite synthesis composition is prepared from a silica source and an organic hydroxide zeolite structure directing agent, coating the substrate with this synthesis composition and heating the substrate and synthesis composition to produce a silica zeolite film on the substrate. Finally, U.S. Pat. No. 6,660,245 B1 discloses a process for removing structured directing agents from a silicalite or zeolite crystal low dielectric constant film by using oxidative attack with a combination of ammonia, water, and hydrogen peroxide at elevated temperatures.
As the above cited art shows, it is generally taught that the zeolite be essentially free of aluminum in order for it to have a low enough dielectric constant. Applicants have determined that zeolite beta would have desirable properties as a low-k dielectric insulator even when it contains a considerable amount of aluminum in the framework (versus other zeolite dielectric materials). Applicants have discovered that it is extremely difficult to synthesize zeolite beta having both a lower aluminum content (about 0.1 wt. % to about 2 wt. % Al) and having crystallites on the order of 5 to 40 nanometers in size. Applicants have developed a process in which zeolite beta containing silicon and aluminum is first synthesized to give crystallites in the nanometer range and than dealuminated thereby removing a portion of the aluminum. A slurry of this lower aluminum containing zeolite beta with crystallites on the order of 5-40 nanometers can now be spin coated onto silicon wafers to form a thin film and then baked to remove the organic template and optionally chemically treated to neutralize any terminal hydroxides and provide a low dielectric constant insulating layer.